Method of making tire tread



i July 9, 1940 -c. E. MAYNARD 2,207,100

METHOD OF MAKING TIRE THE-AD Original Filed May 14, 1936 2 Sheets-Sheet1 NTOR (Imus psmlifimmp 'ATTORNEYS u y 9 1940. f c. E. MAYNARD 2 01,100

METHOD OF MAKING TIRE TREAD Original Filed May 14, 1936 2 Sheets-Sheet 223 INVENTO 634E453 [D64 AYMGRD 24L B @aW M ATTORNEY S Patented July 9,1940 i METHOD OF MAKING TIRE TREAD Charles Edgar Maynard, Northampton,Masa,

assignor, by mesne assignments, to United States Rubber Company, NewYork, N. Y., a corporation of New Jersey Original application May 14,1936, Serial No.

79,758. Divided and this application November 28, 1936, Serial No.113,098

24 Claims.

This invention relates to rubber vehicle tires and their construction,and more particularly to the tread portion of such tires.

It is the principal object of the present invention to provide aneconomical and reliable method bottom of the cuts.

for the production of a tread, or tire having a tread, of the characterdisclosed and claimed in my copending application Serial No. 79,758,filed May 14, 1936, of which application this is'a divi- S1011.

Other and further objects will be apparent in A the followingspecification and claims.

In the accompanying drawings which illustrate the invention- Fig. 1 is aplan view of a portion of a tire tread made according to the invention;

Fig. 2 is a section taken substantially on line 22 of Fig. 1;

Fig. 3 is a view similar to Fig. 2 but showing a modification;

Figs. 4 and 5 are diagrammatic longitudinal sectional views showing thefirst two steps in the general method;

Figs. 6 and 7 are similar views showing one general form of procedurefollowing the steps of Figs. 4 and 5;

Figs. 8 and 9 are similar views showing an alternative form of procedurefollowing the steps of Figs. 4 and 5;

Figs. 10 and 11 are respectively sectional views of two forms of gumstrip;

Fig. 12 is a perspective view of a tread strip embodying the invention;and

Fig. 13 is a diagrammatic view of means for carrying out the method as asubstantially continuous operation.

It will be understood that the drawings are not to scale and parts suchas the thickness of the gum strips used and the sectional width of thecut openings have been exaggerated for the sake of clearness. Both thesectional width and the thickness of the gum strip will in practice hevery small.

It has previously been proposed, as a means of securing a non-skidtread, to mold and vulcanize the tread in the form of circumferentialribs and thereafter cut the ribs transversely to a depth approximatelyone-third of the depth of the ribs. This procedure is subject to anumber of objections. Among these may be mentioned the fact thatvulcanized rubber when out is subject to chipping and tearing at the cutedges and there is a further tendency for the tread to crack at the Tominimize this tendency it has been necessary to limit the depth of cutsto approximately one-third of the depth of the rib, or other treaddesign element which may be used, with the result that the non-skideffect lasts only during one-third of the life of the tread.

it is possible to subject the worn tread to a recutting operation, butthis adds to the expense, and many purchasers rather than go to thebother of returning the tires for recutting will continue to run thetires with smooth ribs, with a consequent road hazard from skidding. Afurther objection lies in the fact that vulcanized rubber is difilcultto cut and since the tire is complete at the time of the cuttingoperation, any imperfection or failure in the cutting results in theloss of the entire production cost of the tire.

As will be evident from the following specification, all of the abovementioned dimculties are overcome by my invention and many advantagesobtained in improved operation, in quality, and uniformity of theproduct, and in manufacturing costs.

Referring to the drawings, I indicates generally the tread of apneumatic tire, the tire carcass being conventionally indicated at 2 inFigs. 2 and 3. As shown, the tread design comprises circumferential ribs4, but any suitable tread configuration may be used. The ribs andunderlying portion of the tread are provided with a multiplicity oftransverse cuts 5, see Figs. 1 and 2, which extendinwardly anddownwardly from the tread shoulders. If preferred, the cuts may extendstraight across through the shoulders, as indicated at 5 in Fig. 3.

According to my invention these cuts are formed in the tread portion ofthe tire, either before or after the tread is assembled on the carcassor after the carcass is expanded, but in any event before the tire isvulcanized. The cuts may beformed by means of any suitable knife. Aswill be later referred to, the knife may advantageously be heated or aheated wire may be used.

Referring to Figs. 4 to 9 inclusive, the cuts ii having been made in theunvulcanized tread, the

tread is flexed as shown in Fig. 5, to open the cuts. This flexing maybe done as a separate manipulation before or after the tread is placedon the tire. When the tires are constructed fiat or semi-fiat, theexpansion of the tire from flat or semi-fiat band form to tire shapeserves to flex the cuts open. 9

Figs. 6 and 8 illustrate two alternative procedures from this point. Asillustrated in Fig. 6, I propose to fill the opened cut with alubricating material such as powdered or liquid soapstone, as indicatedat 6. When the flexing force like.

is released, or partially released, see Fig. '7, sumcient soapstone isgripped and held in the cut to prevent joining of the sides of the cutduring the subsequent vulcanizing. The tire casing is vulof cut surfacesas in the prior practice, prevents chipping of the edges or splitting atthe bottom so that the clefts may be carried, as

shown, below the depth of the ribs so that the non-skid function of theclefts throughout the life of the tread.

A modified procedure, and in some ways the preferable one, is shown inFigs. 8 and 9. with the cuts 5 flexed open, as shown in Fig. 5, a stripof gum stockB is inserted in the cut. The gum stock may includesuflicient pigment to give it a color the same as the tread or acontrasting color may be used. The gum strip may be rectangular incross-section or may be given a cross-section such as shown at 8' and 8in Figs. 10 and 11 respectively. Instead of gum stock, the cut may befilled with rubber cement, liquid latex, or a rubber dough, theessential feature being that the inserted rubber material shall berelatively soft, pliable, and deformable, as compared with the treadstock, when both have been vulcanized. It will be understood that thefiller material bonds with the adjacent tread stock upon vulcanizationbut permits, because of the flexibility of the filler,

relative movement between the blocks into which the filled clefts dividethe ribs. In use the soft filler tends to wear faster than the tread andretreats as the tread wears, but the depth of the opened clefts soresulting is never great enough to afford lodgment to sand or stones.This freedom from the liability of picking up sand and stones comprisesone important advantage of this form of my invention. A furtheradvantage of this. form is that the cutting and filling may be carriedout as a continuous operation on a tread strip which is later cut tolength in the usual manner for use in conventional building operations.Where a lubricant is used to form free walled clefts, as previouslydescribed, substantial carehas to be used if the work isdone on thetread in strip form to prevent lubricant coming in contact with theunder side of the tread strip where its presence might prevent properadhesion of the tread to the carcass. This danger is not present whenthe cuts are filled with gum or the In Fig. 12 a tread strip is shown inflat form, the cuts being shown at 5'. It will be understood that thecuts 5 may be made either before or after the strip has been cut tolengthand rubber inserts or lubricating material placed in the cutseither before or after such cutting to length and either before or afterthe tread length is placed on the tire carcass.

Fig. 13 discloses diagrammatically one way of carrying out a continuouscutting and filling of a tread strip. As there shown, the tread strip I0is guided around a roll 20, thus tensioning the outer surface. As itpasses over and is bent around roll 20 a knife 22 cuts the strip to,thedesired depth to form cuts 5'. The strip then passes beneath a guideroll 23 and over a roll 24 which isof sufficiently small diameter toflex the strip and open the cuts 5' for the reception 3 continues thefiller or a lubricating material, as indicated at 25.

The use of a heated knife or wire as a means for making the cuts hasbeen mentioned above. The immediate effect of the heated knife or cutteris to soften the rubber and, if the'gum strips are immediately inserted,bonding of the tread and gum stock surfaces is facilitated. The use ofsuch cutting means may also be employed advantageously when it isdesired to form open clefts, since the heat of the knife or wire has atendency to start a superficial vulcanization if given time andopportunity, especially where high speed accelerators are used, thusaiding whatever lubricant is used in preventing adhesion of the walls ofthe clefts during subsequent vulcanization. ,The tendency of the sulphurin the rubber compound to bloom on the surface of the cuts also aids inpreventing adhesion of the walls.

If the out treads are permitted to age, even for 53 a comparativelyshort period before being vulcanized, the tendency of adhesion of thewalls is lessened.

The cuts or clefts may be equally spaced about the circumference of thetire but preferably an unequal spacing is used to afford quietoperation.

It will be seen that'whether the zones of separation between theindependently acting portions of the ribs are constituted by open cleftsor integral insets ofsoft rubber material, these zones are congenitalwith the tire tread and are, therefore, part of the tire as the latteris taken from the vulcanizing mold.

While the invention has been described as applied to a pneumatic tire,it may also be employed in the construction of solid or cushion tires.

I claim:

1. The method of constructing a tire casing which comprises forming aplurality of knifelike cuts transversely of the unvulcanized rubberstrip which is to become the tread of the casing, flexing said strip toopen said cuts, inserting material into said cuts to preserve at saidcuts zones of relative movement and flexibility between the portions ofthe strip between the cuts, assembling the strip on the tire carcass inthe usual manner and vulcanizing the casing in a conventional tire moldwhereby said zones portion, forming a plurality of spaced cuts ex--tending transversely of the tread, flexing the casing to open the cuts,inserting material into said cuts to preserve zones of relative movementbetween the portions of the tread between the cuts,

and'vulcanizing the casing in a conventional the mold whereby said zonesbecome congenital parts of the completed tire.

3. The method of constructing a tire casing which comprises assemblingthe unvulcanized casing in a conventional manner as a band of lessdiameter than the tread diameter of the finished casing, forming aplurality of spaced cuts extending transversely of the tread, expandingthe band to tire shape and thereby openthe cuts, inserting material intosaid cuts to preserve zones 01' relative movement between the portionsof the tread between the cuts, and vulcanizing the casing in aconventional tire mold whereby said zones become congenital parts of thecompleted tire.

4. a method of manufacturing pneumatic tires having the tread formedwith cuts which impart to the tire anti-skidding properties,characterized by forming the cuts in the tread prior to the introductionof the tire into a vulcanizing mold 6 and introducing into the cuts amedium which will prevent the walls of the cuts from sticking togetherduring the operation of vulcanizing the tire in the mold, and thereafterintroducing the tire into the mold and vulcanizing it therein.

10 5. A method as claimed in claim 4 wherein the cuts are formed in thetread of an already shaped tire.

6. A method as in claim 4, wherein the tire is built at least partiallyflat and subsequently shaped, the cuts being formed in the tire prior tothe shaping operation.

d 7. A method as in claim 4'wherein a rubber strip to form the tread isfirst produced which is afterward applied to a carcass to form thecomplete tire and wherein the cuts are formed in the rubber strip priorto the application of the latter to the carcass.

8. A method as in claim 4 wherein the cuts extend only over the centralportion of the width of the tread.

9. A method as in claim 4 wherein 'theantisticking medium is appliedwhen the tread is in curved or bent condition with the cuts inconsequence open.

'10. The method of constructing a tire casing which comprises forming in'a tread strip of homogeneous tough wear-resisting tread rubber, aplurality of transverse, circumferentially spaced knife-like cuts,inserting in said cuts material to maintain the walls of said cutsseparated during the subsequent vulcanizing of the tire, applying saidtread strip to a tire carcass to form the tread portion of the casingand thereafter introducing the casing into a mold and vulcanizing ittherein. 40 11. The method of constructing a tire casing which comprisesforming a plurality of knife-like cuts transversely of the unvulcanizedhomogeneous strip of tough wear-resisting tread rubber which is tobecome the tread of the casing, flexing the strip to open said cuts,inserting therein a rubber material to prevent complete closure of theout upon release of the strip and which will be more flexible aftervulcanization than the body of the tread after the latter is vulcanized,assembling the strip on the tire carcass in the usual manner andvulcanizing the casing in a conventional tire mold whereby said insertedrubber material becomes integrally bonded with the adjacent body of thetread to form flexible in- 65 sets permitting independent movement ofthe tread portions intermediate said insets.

12. The-method of constructing a tire casing which comprises forming aplurality of knife-like cuts transversely of the unvulcanized homogenecoous strip of tough wear-resisting tread rubber which is to become thetread of the casing, inserting in said cuts a thin strip of homogeneous,rubber material which will be more flexible after vulcanization thanthe body of the tread after the 65 latter is vulcanized, assembling thestrip on the tire carcass and vulcanizing the casing.

v 13. The method of constructing a tire casing which comprises forming aplurality of knifelikecuts in the unvulcanized homogeneous strlp 70 oftough wear-resisting tread rubber which is to become the tread of thecasing, inserting in said after vulcanization than the tread body of thetread. after the latter is vulcanized, the amount 76 of materialinserted being sufficient to maintain the walls of the cuts out ofcontact and permit relative movement thereof but insuiilcient to causethe inserted material to. wear substantially below the surface of theadjacent tread rubber in service, assembling the strip on the tire car-5 cass and vulcanizing the casing hereby the inserted material becomesbonded wi h the adjacent body of the tread.

14. The method of constructing the tread portion of a tire casing whichcomprises forming a 10 plurality of knife-like cuts in anunvulcanizedhomogeneous strip of tough wear-resisting tread rubber,applying tension to the cut portion of the tread to spread the cuts,inserting in said cuts a rubber material less wear-resisting but moreflex- 15 ible .than the rubber forming the body of the strip when bothare vulcanized and releasing the tension on the strip.

15. The method of constructing the tread portion of a tire casing whichcomprises forming a '20 plurality of knife-like cuts in an unvulcanizedhomogeneous strip of tough wear-resisting tread rubber, applying tensionto the cut portion of the tread to spread the cuts, inserting in saidcuts a rubber material less wear-resisting but more 25 flexible than therubber forming the body of the strip when both are vulcanized, theamount of the material inserted being suflicient to maintain the wallsoftlie cuts out of contact and permit relative movement thereof butinsumcient to cause 30 the inserted material to wear substantially belowthe surface of the adjacent tread rubber in service.

16. The method of constructing a tire casing which comprises flexing theunvulcanized homo- 35 geneous strip of tough wear-resisting tread rubberwhich is to become the tread of the tire to place the outer surfaceunder tension, forming cuts in the so tensioned strip, inserting in saidcuts a more flexible less wear-resisting rubber (0 material than thatforming the body of the strip and possessing sumcient immobility whenheated to vulcanizing temperature and subject to molding pressure toretain its location in said cuts, releasing the tread strip fromtension, assembling 4,5 the strip on a tire carcass and vulcanizing thetire.

17. The method of constructing a tire-tread which comprises forming aplurality of cuts in the tough wear-resisting rubber body of the tread60 while the latter is unvulcanized, filling said cuts with a moreflexible less wear-resisting rubber material than that forming the bodyof the tread and which possesses suflicient immobility when heated tovulcanizing temperature and subjected to molding pressure to retain itslocation in said cuts, and vulcanizing the so formed tread.

18. The method of constructing a tire casing which comprises forming aplurality of knifelike cuts in an unvulcanized homogeneous strip oftough wear-resisting tread rubber, inserting in said cuts a vulcanizablematerial which will be more flexible and deformable after vulcanizationthan the tread rubber after the latter is vulcanized, assembling thestrip on a tire carcass and vulcanizing the completed casing whereby theinserted material becomes permanently bonded with the adjacent body ofthe tread.

19. The method of constructing a tire casing which comprises forming aplurality of knifelike cuts transversely of an unvulcanized homocuts arubber material which will be more flexible geneous strip of toughwear-resisting tread rubber, inserting in said cuts a vulcanizablematerial which will be more flexible and deformable I aftervulcanization than the tread rubber after the latter is vulcanized,assembling the strip on a tire carcass and vulcanizlng the completedcasing in a mold to form open circumferential grooves in the treadportion of the tire.

20. The method of constructing a tire casing.

which comprises forming a plurality of knife-like cuts transversely ofan unvulcanized homogeneous strip of tough wear-resisting tread rubber,inserting in said cuts a vulcanizable material which will be moreflexible and deformable after vulcanization than the tread rubber afterthe latter is vulcanized, assembling the strip on a tire carcass andvulcanizing the completed casing in a mold to form open circumferentialgrooves in the tread portion of the tire of less height than the depthof the cuts made in the unvulcanized tread strip so that the materialinserted in the cuts will penetrate the tire tread to a depth below theopen grooves molded in the tread.

21. The method of constructing a rubber tire tread which comprisesforming a plurality of cuts in the tough wear-resisting rubber of thetread while the latter is unvulcanized, filling said cuts with avulcanizable material which will be more flexible and deformable aftervulcanization than the tread rubber after the latter is vulcanized, andvulcanizing the tread. I

22. The method of constructing a tire casing which comprises, bending ahomogeneous strip of unvulcanized tough wear-resisting tread rubberlongitudinally to place the outer portion under tension, formingknife-like cuts in the so tensioned strip, transversely thereof, bymeans of a heated knife, inserting edgewise in the cuts, while the wallsof the latter are tacky from the heat of the knife, ribbon-like stripshaving a width substantially equal to the depth. of the cuts, formed ofan unvulcanized homogeneous rubber material which will be more flexible,deformable and less wear-resisting after vulcanization than the treadrubber after the latter is vulcanized releaslng the tread from tensionto cause the ribbon-like strips to be gripped between the tacky walls ofthe cuts, placing the so formed composite strip on a tire carcass andvulcanizing the completed casing in a mold to form open circumferentialgrooves in the tread portion of the tire.

23. The method of constructing the tread portion of a tire casing whichcomprises, bending a homogeneous strip of unvulcanized toughwearresisting tread rubber longitudinally to place the outer portionunder tension, forming knii'elikecuts in the so tensioned strip,transversely thereof, by means of a heated knife, inserting edgewise inthe cuts, while the walls of the latter are tacky from the heat of theknife, ribbonlike strips having a width substantially equal to the depthof the cuts, formed of an unvulcanized homogeneous rubber material whichwill be more flexible, deformable and less wear-resisting aftervulcanization than the tread rubber after the latter is vulcanized,releasing the tread from tension to cause the ribbon-like strips to begripped between the tacky walls of the cuts, placing the so formedcomposite strip on a tire carcass and vulcanizing the completed casingin a mold to form open circumferential grooves in the tread portion ofthe tire,'of less height than the depth of the cutsmade in theunvulcanized tread strip so that the material inserted in the cuts willpenetrate the tiretread to a depth below the open grooves molded in thetread by the ribs.

24. The method of preparing the tread portion of a tire casing forapplication to a tire carcass which comprises, forming a plurality ofcuts in a homogeneous strip of unvulcanized, tough wear-resisting treadrubber, filling each of said cuts by inserting edgewise therein ribbonsof an unvulcanized but vulcanizable material which will be more flexibleand deformable but less wear-resisting after vulcanization than thetread rubber after the latter is vulcanized.

fiHARLES WAR MAYNARD.

